It's well known that "Emperor Qin built the Great Wall". But the history of the Great Wall is not that simple. Emperor Qin was not the first to build the Great Wall... or the last. There are many sections in different places, built with different materials, and built in different dynasties.

When the Great Wall was built

Dynasty

Who built

The (Pre-) Warring States Period (770–221 BC)

Overlords built walls

The Qin Dynasty (221–207 BC)

The First Emperor of Qin linked the Great Wall

The Han Dynasty (206BC–220AD)

Han Wudi extended west to Yumen Pass

The Ming Dynasty (1368–1644)

Qi Jiguang rebuilt the Great Wall

The (Pre-) Warring States Period — Overlords Built Walls

A Qi State duke first built walls to prevent invasion from other states.

Before the unification of China, there were many warring states. Battles between states happened frequently to expand territory. Therefore, the princes and overlords began to build high walls to keep intruders out in the Seventh Century BC.

According to historical records, the Qi State was the first state to build such walls in 656 BC. During the Spring and Autumn Period, Qi Huangong (Duke Huan of Qi) became a Qi overlord (reigned 685–643 BC; mainly in today's Shandong Province). He ordered that walls be built to prevent incursions by the Chu State, south of Qi. The walls of Qi were mainly built with flat stones.

From then on, princes and overlords from other states began to build walls on their borders, and high mountain watchtowers to defend against invasion, mostly during the Warring States Period (475–221 BC).

The Qin Dynasty — The First Emperor Linked the Great Wall

The Great Wall was built to prevent invasion from northern nomadic tribes.

Emperor Qin unified state walls to secure China's northern border.

After the unification of China in the beginning of the Qin Dynasty (221–207 BC), China's first emperor, Qin Shihuang (you must have heard of his Terracotta Army), linked the walls of the three northern states (Qin, Zhao, and Yan). This formed the first "Wan-Li Changcheng" (万里长城 'Ten-Thousand-Li Great Wall' i.e. the first '5,000-Kilometer Great Wall': a li is half a kilometer).

Sui, Tang, Song, and Yuan Emperors Modified the Great Wall

After the re-unification of China, the emperors of the following dynasties — Sui (581–618), Tang (618–907), Song (960–1279), and Yuan(1115–1234) — rebuilt, modified, and extended the Great Wall to protect the Chinese Empire from northern invaders. Today, in some areas, two walls built in two different dynasties can be seen running side by side.

The Ming Dynasty — Qi Jiguang Rebuilt the Great Wall

Beautiful scenery of Jinshanling Section

Most of today's Great Wall was built or restored in the Ming Dynasty.

In order to consolidate the northern border, after reclaiming China from the Mongol-led Yuan Dynasty (1279–1368), Emperors of the Ming Dynasty (1368–1644) never stopped building the Great Wall.

The most well-known sections (Simatai, Mutianyu, Jinshanling, Badaling, etc.) were all built or strengthened by Qi Jiguang (1528–88, a hero general who also saved China's coastlands from Japanese pirates).

The Ming Great Wall runs from Jiayuguan on western China's Silk Road to Shanhaiguan on eastern China's Bohai Gulf coast.

The Qing Dynasty — The End of Great Wall Building

Emperor Kangxi

The emperors of the Qing Dynasty (1644–1911) didn't build the Great Wall and even forbade it: they were Manchurians, who the Great Wall was built to keep out.

It's said that when Emperor Kangxi (1654–1722) saw the Great Wall, he reasoned that the era of Great-Wall-building emperors and enmity with northern neighbors was over. Moreover, Great Wall construction cost lots of money and manpower, which was bad for his people. He believed that the only way to protect China was to gain international support, instead of border battles.

So second Qing Emperor Kangxi ordered that the Great Wall never be built, and there was almost no Great Wall built from the end of Ming Dynasty.